Field effect transistors, such as n-channel power metal-oxide-semiconductor field effect transistors (MOSFETs), are generally desired to have low conduction and switching losses in many power applications. Field effect transistors should also be rugged enough to prevent the parasitic bipolar junction transistor from turning on under high current conditions, such as unclamped inductive switching (UIS). The failure of MOSFETs during UIS is due to activation of the parasitic NPN bipolar transistor in breakdown mode.
The parasitic NPN bipolar junction transistor (BJT) in the power MOSFET is composed of the n+-source, p-body and n−-drift, and these three regions also act as the emitter, base and collector of the parasitic bipolar junction transistor, respectively. The p-body is connected to the source electrode through a p+ region, and the n+-source/p-body junction is shorted at the source electrode of the device. The n+-source/p-body junction will not be forward biased at the static on-state or off-state of the power MOSFET. However, under transient conditions such as avalanche operation of the power MOSFET, reverse recovering of the body diode and fast rising of drain-to-source voltage, current will flow through the p-body to the source electrode. This will cause a potential drop across the resistance of the p-body. If the current flow is large enough and the potential drop is significantly high enough, the n+-source/p-body junction will be forward biased, and the parasitic bipolar junction transistor will be activated. The activation of the parasitic bipolar junction transistor will cause a second-breakdown behavior of the power MOSFET, and thermal runaway can also result.
The above-described deficiencies of conventional field effect transistors are merely intended to provide an overview of some of problems of current technology, and are not intended to be exhaustive. Other problems with the state of the art, and corresponding benefits of some of the various non-limiting embodiments described herein, may become further apparent upon review of the following detailed description.